{ INFORMATICS.MCCME.RU
  Problem statement: http://informatics.mccme.ru/moodle/mod/statements/view3.php?chapterid=3076
  Verdict: Accepted
}
uses SysUtils, Math;
 
var
	a,b:int64;
 
begin
reset(input,'input.txt');
rewrite(output,'output.txt');
read(a,b);
while a>b do begin
	if odd(a) then begin
		writeln(-1);
		dec(a);
	end else begin
		if a div 2>=b then begin
			writeln(':2');
			a:=a div 2;
		end else begin
			writeln(-1);
			dec(a);
		end;
	end;
end;
end.